Dynamic Measurement And Analysis Of Air Gap Variations In Large Hydroelectric Generators

This paper presents the development and application of a new fibre-optics instrumentation system for accurate measurement and analysis of the dynamic air gap behaviour of large hydroelectric generators. The system uses a passive reflective fibre-optics sensor which is immune to EMI and functions correctly on an excited operating generator. Air gap tests were performed on four 184 MV. A, 15.6 m stator bore diameter generators with 16 radial stator support rods. One of these units at B. C. Hydro´s Peace Canyon Project suffered rotor-stator contact damage during commissioning in November 1979. Thirty-two air gap measurements were made around the stator during consecutive revolutions, at precisely repeatable points at, and midway between, the noted support rods. These measurements were used to produce a series of polar coordinate air gap maps which facilitated very fine trend analysis of the critical modes of generator operation. These tests and the interpretation of the data, which assisted in the solution of specific problems, are presented.